1. Field of the Invention
The invention generally relates to devices and methods for manufacturing a continuous center core wrapped with reinforced thermoplastic having very long, fully dispersed and fully wet out filaments.
2. Description of the Related Art
Processes are known for combining reinforcing fiber strands with thermoplastic resin to form reinforced plastic composites. U.S. Pat. Nos. 4,439,387 and Re. 32,772 sharing common inventorship herewith, and incorporated by reference herein in entirety, disclose the embedding of thermoplastic resin in reinforcing fiber strands as they are drawn through a forming die having a convoluted passage, in the presence of molten thermoplastic resin introduced from an extruder. The extrusion product of that process comprises an elongated bar or rod having a continuous length of reinforcing fiber encased within thermoplastic resin. That preformed composite may be inserted into a die of an injection molding machine, and utilized as an insert in a compound, composite product comprising an additional layer of thermoplastic resin molded over the insert. It is also known to cut the extrudate rod from the aforesaid forming die into short lengths for use as molding pellets. In the process of the aforesaid United States patents, the extruded rod comprising a fiber/resin composite is immediately cooled, prior to final forming and cutting to desired lengths.
U.S. Pat. No. 5,185,117, also having identity of inventorship herewith and incorporated by reference herein in its entirety, discloses a process for compounding thermoplastic resin and fiber strands in an extruding compounder. According to the process of that patent, melted thermoplastic resin is introduced into the compounding extruder along with reinforcing fiber strands. The resulting extrudate consists of a molten mass of thermoplastic resin having discrete lengths of fiber strands randomly dispersed therein. This hot mixture may then be fed directly into a preform device to produce a measured preform for use in a compression molding machine. In the disclosed process of the '117 patent, the fiber strands are precut to desired lengths, before being introduced into the extruding compounder. The process and apparatus further requires a loss-in-weight scale to accurately measure predetermined quantities by weight of reinforcing fiber strands to be controllably introduced into the compounding extruder in the presence of thermoplastic resin. A separate loss-in-weight feed scale assembly is required to accurately convey predetermined amounts by weight of the thermoplastic resin into the compounding extruder for mixing in the desired proportions with the reinforcing fiber strands. The loss-in-weight scales necessarily add to the cost and complexity of the compounding apparatus.
U.S. Pat. No. 4,616,989 discloses an apparatus for incorporating glass fiber strands into thermoplastic resins in which a premixing chamber is utilized to initially mix glass fiber strands with molten resin. This mixture is then fed into a two-stage screw-type extruder to complete the mixing of the fiber strands and resin. The resin-fiber mass as discharged from the final extruder is passed through a forming die having a plurality of orifices. This serves to form the material into elongated filaments of glass fiber reinforced resin which are then cooled, and then granulated for use as a molding compound.
U.S. Pat. No. 2,877,501 to Brandt discloses a process for forming granules comprised of glass fiber strands coated with a molding plastic, which are intended for use as feed stock for an injection molding machine. In the Brandt process, fiber strands are pulled through an orifice within which they are coated with a resin material.
U.S. Pat. Nos. 6,186,769; 6,431,847; 6,604,929; 6,676,864; 6,875,385; and 7,169,340, each having common assignment and ownership herewith and each patent being incorporated herein in its entirety, disclose a compact and efficient apparatus and processes for formulating a mixture of fiber reinforced resin for molding purposes are operatively effective for preparing a molding material comprised of fiber reinforced resin for immediate introduction into a molding machine such as an injection molding machine, a compression molding press, a transfer mold, a blow mold, a profile extrusion machine or an inject compression molding machine at the same site where the fiber-resin mixture is made. The referenced patents also disclose formulating a mixture of fiber reinforced resin for molding purposes operate in a controlled and accurate discontinuous manner. Though these references provide distinct advantages over the art, the process and apparatus disclosed therein operate at relatively high pressures, i.e., ranging from 4,000 to 40,000 psi resulting in relatively high shear and speed as the entrained fiber strands move under tension through the coating die. Exemplary speeds are between 80 to 250 feet per minute when the resin is subjected to pressures between 12,000 and 14,000 psi. The high speed and pressure results in, inter alia, shearing forces that cause the fiber strands to break apart. Moreover, the fiber bundles are not efficiently unbundled and as a result remain undispersed, resulting in encapsulation of multiple fibers, without full wet out of individual fibers. Indeed, evaluation of the PUSHTRUSION™ apparatus and process, described by the aforementioned U.S. Pat. Nos. 6,186,769; 6,431,847; 6,604,929; 6,676,864; 6,875,385; and 7,169,340, results in fiber lengths of 3 to 5 mm.
None of the art discloses or suggests apparatus or methods for dispersing the fiber roving so that the thermoplastic material thoroughly wets or impregnates the glass filaments without breaking the very thin glass filaments at the 3 to 5 mm length range.
Longer fibers provide significant improvement in, inter alia, modulus, strength and impact resistance as compared with shorter fibers. According to Thomason & Vlug these mechanical properties are not fully optimized, i.e., all three measures at 95% of potential, until fiber length is about 25 mm, with modulus, strength and impact resistance steadily increasing with lengths upwards of 50 mm. Related to fiber length is the dispersion and distribution of individual fibers. Fully dispersing and distributing individual fibers without breaking and with full wet out is highly advantageous and provides a reinforcing matrix in molded parts that the prior art has not achieved. Moreover, fuller dispersion of the fiber bundles results in fewer cosmetic blemishes; none of the prior art discloses or suggest apparatus or methods for fully dispersing and wetting out the individual fibers with thermoplastic substrate while providing very long, unbroken fibers.
Moreover, present reinforcing elements used in construction projects typically comprise rebar and the like which is normally manufactured from steel. Existing reinforcing elements such as rebar are heavy, subject to corrosion and weakening.
The present invention addresses these, inter alia, problems.